Comment by stackghost

RFC 1459 originally stipulated that messages not exceed 512 bytes in length, inclusive of control characters, which meant the actual usable length for message text was less. When the protocol's evolution was re-formalized in 2000 via RFCs 2810-13 the 512-byte limit was kept.

However, most modern IRC implementations support a subset of the IRCv3 protocol extensions which allow up to 8192 bytes for "message tags", i.e. metadata and keep the 512-byte message length limit purely for historical and backwards-compatibility reasons for old clients that don't support the v3 extensions to the protocol.

So the answer, strictly speaking, is yes. IRC does still have message length limits, but practically speaking it's because there's a not-insignificant installed base of legacy clients that will shit their pants if the message lengths exceed that 512-byte limit, rather than anything inherent to the protocol itself.